Memory circuits, systems, and methods for accessing the memory circuits

ABSTRACT

A memory circuit includes at least one memory cell for storing a charge representative of a datum. The memory cell is coupled with a word line and a bit line. A sense amplifier is coupled with the bit line. The sense amplifier is capable of precharging the bit line to a first voltage that is substantially equal to and higher than a threshold voltage (V t ) of a first transistor of the sense amplifier.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of U.S. Provisional PatentApplication Ser. No. 61/237,561 filed on Aug. 27, 2009 which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the field of semiconductorcircuits, and more particularly, to memory circuits, systems, andmethods for accessing the memory circuits.

BACKGROUND

Memory circuits have been used in various applications. Conventionally,memory circuits can include DRAM and SRAM circuits. A DRAM circuitincludes a plurality of memory cells. For conventional dynamic memorycells in which arrays of capacitive storage memory cells are provided,each memory cell has an access transistor. Data stored in such memorycells is actually a charge stored on a small capacitor. When the data isto be output, the access transistor is activated by a word line (WL)coupled with the gate or control terminal of the transistor. The accesstransistor can couple the capacitor to a bit line (BL) coupled to asense amplifier for sensing the voltage of the capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the numbers and dimensions of the various features may bearbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic drawing illustrating an exemplary memory circuit.

FIG. 2 is a flowchart illustrating an exemplary method for accessing adatum represented by a charge stored in at least one memory cell of amemory circuit.

FIG. 3 is a schematic drawing illustrating waveforms for accessing amemory cell storing a datum “0”.

FIG. 4 is a schematic drawing illustrating waveforms for accessing amemory cell storing a datum “1”.

FIG. 5 is a schematic drawing illustrating another exemplary memorycircuit including a precharge transistor.

FIG. 6 is a schematic drawing showing a system including an exemplarymemory circuit.

FIG. 7 is a schematic drawing illustrating waveforms for access a memorycell storing a datum “0”, according to some embodiments.

DETAILED DESCRIPTION

A conventional 3-transistor single ended sense amplifier has beenproposed to sense data stored in DRAM cells. The conventional3-transistor single ended sense amplifier has a PMOS transistor coupledwith an NMOS transistor that are disposed between power voltages VDD andVSS. A gate of the PMOS transistor is coupled with a read bit line(RBL). A gate of the NMOS transistor is coupled with a write bit line(WBL). The conventional 3-transistor single ended sense amplifier alsohas a sensing NMOS transistor coupled between the read bit line RBL andthe write bit line WBL. A gate of the sensing NMOS transistor is coupledto the bit line BL.

For sensing a datum stored within the DRAM cell, the bit line BL isprecharged to the power voltage VSS. After precharging the bit line BL,the charge stored within the DRAM cell is charge shared with the bitline BL. If no substantial charge is stored within the DRAM cell, thevoltage of the bit line BL may be slightly pulled up due to a leakagecurrent. The slightly pulled-up voltage of the bit line BL does not turnon the sensing NMOS transistor. The turned-off sensing NMOS transistorisolates the read bit line RBL from the write bit line WBL. The read bitline RBL having a voltage, e.g., VDD, is free from being coupled withthe write bit line WBL having a voltage, e.g., VSS. A global bit lineGBL coupled with the read bit line RBL is free from sensing asubstantial voltage change on the read bit line RBL. The datum outputfrom the global bit line GBL is determined as “0”.

If a substantial charge is stored within the DRAM cell, the voltage ofthe bit line BL can be substantially pulled up from the power voltageVSS due to the charge sharing. The pulled-up voltage of the bit line BLturns on the sensing NMOS transistor. The turned-on sensing NMOStransistor couples the read bit line RBL having a voltage, e.g., VDD,with the write bit line WBL having a voltage, e.g., VSS. The voltage ofthe read bit line RBL is substantially pulled down. A global bit lineGBL coupled with the read bit line RBL senses a substantial voltagechange of the read bit line RBL. The datum output from the global bitline GBL is determined as “1”.

As noted, the sensing of the datum stored within the DRAM cell isrelated to the threshold voltage (V_(t)) of the sensing NMOS transistor.It is found that the threshold voltage V_(t) of the sensing NMOStransistor may change due to variations of semiconductor manufacturing.Due to the variation of the threshold voltage V_(t) of the sensing NMOStransistor, a voltage of the bit line BL may turn on the sensing NMOStransistor in some cases. In other cases, the same voltage of the bitline BL may not turn on the sensing NMOS transistor.

As noted, the conventional 3-transistor single ended sense amplifieruses a pair of the read bit line RBL and the write bit line WBL forsensing the voltage change of each bit line BL. A routing of the readbit line RBL and the write bit line WBL may use two or more metal layersand vias. The routing of the read bit line RBL and the write bit lineWBL is complicated.

It is also found that the conventional 3-transistor single ended senseamplifier consists of the PMOS transistor and two NMOS transistors oneof which is the NMOS sensing device. A dimension of the PMOS transistoris larger than that of each of the NMOS transistors. A large spacebetween the NMOS transistors is used to accommodate the PMOS transistor.A large area of the conventional 3-transistor single ended senseamplifier is used.

Based on the foregoing, memory circuits, systems, and methods foraccessing data stored within the memory circuits are desired.

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

FIG. 1 is a schematic drawing illustrating an exemplary memory circuit.In FIG. 1, a memory circuit 100 can include a memory array 101 includinga plurality of word lines and a plurality of bit lines. The memorycircuit 100 can be a dynamic random access memory (DRAM) circuit, anembedded DRAM circuit, a static random access memory (SRAM) circuit, anembedded SRAM circuit, a non-volatile memory circuit, e.g., FLASH,EPROM, E²PROME, a field-programmable gate array circuit, a logic arraycircuit, and/or other memory circuit. The memory array 101 can includeat least one memory cell 101 a. The memory cell 101 a can be coupledwith a bit line (BL) and a word line (WL) of the memory array 101. Forembodiments using a DRAM cell, the memory cell 101 a can include amemory transistor T_(c) and a capacitor C_(c). The capacitor C_(c) iscapable of storing a charge representative of a datum, e.g., “0” or “1”.

It is noted that though only one memory cell 101 a is depicted, anothercell (not shown) can be placed at the intersection of each of aplurality of word lines and the bit lines. A portion of the memory array101 may have 8, 16, 32, 64, 128 or more columns that can be arranged inword widths. In some embodiments, the word lines can be laid outsubstantially orthogonally to the bit lines. In other embodiments, otherarrangements of the word lines and bit lines can be provided.

Referring to FIG. 1, the memory circuit 100 can include a senseamplifier 110. The sense amplifier 110 can be coupled with the bit lineBL. The sense amplifier is capable of precharging the bit line BL to avoltage that is substantially equal to or higher than a thresholdvoltage V_(t) of a first transistor, e.g., transistor 111, of the senseamplifier 110. The transistor 111 can be referred to as a sensingdevice. In some embodiments, the voltage that is substantially equal toor higher than the threshold voltage V_(t) of the transistor 111 canmean that the voltage is between about the threshold voltage V_(t) ofthe transistor 111 and about half of an internal power voltage (VDD). Inother embodiments, the voltage that is substantially equal to or higherthan the threshold voltage V_(t) of the transistor 111 can mean that thevoltage can desirably fully or partially turn on the transistor 111. Instill other embodiments, the threshold voltage V_(t) of the transistor111 can be between about 250 mV and about 350 mV. It is noted that thethreshold voltage V_(t) of the transistor 111 described above is merelyexemplary. The threshold voltage V_(t) of the transistor 111 can varydue to the change of the processing technology. The scope of theinvention is not limited thereto.

In some embodiments, a gate of the transistor 111 can be coupled withthe bit line BL. A first source/drain (S/D), e.g., S/D 111 a, of thetransistor 111 can be coupled with a global bit line GBL. A secondsource/drain (S/D), e.g., S/D 111 b, of the transistor 111 can becoupled with a first signal line, e.g., signal line SL1. In someembodiments, the global bit line GBL can be coupled with the senseamplifier 110 through a use of a column select control line (not shown)and/or column select coupling transistors (not shown). In this manner,many columns of memory cells may be arranged in sub-arrays andselectively coupled to the global bit line GBL.

Referring to FIG. 1, the sense amplifier 110 can include a secondtransistor, e.g., transistor 113. The transistor 113 can include a firstsource/drain (S/D), e.g., S/D 113 a, coupled with the global bit lineGBL. A second source/drain, e.g., S/D 113 b, coupled with the bit lineBL. A gate (not labeled) of the transistor 113 can be coupled with asecond signal line, e.g., signal line SL2. In some embodiments, thesignal line SL2 can receive a bank select signal. In other embodiments,the transistor 113 can have a threshold voltage that is higher than thatof the transistor 111.

Following are descriptions regarding methods for accessing a memorycell. A dynamic memory can be refreshed periodically because the storedcharge in the cells may leak away over time. Timing circuitry (notshown) can track the time elapsed since the last access to the memorycells and will cause the circuit to “refresh” the cells if desired.Refresh can be done, for example, by performing a read followed by arestore or “write back” cycle to the cells.

It is noted that any read of a memory cell of the memory cell 101 a mayresult in charge leakages. The cell can be restored or rewritten at theend of the cycle. A “write” can be simply a read cycle with write dataimpressed on the respective local bit line during the “restore” portionof the cycle. For a write, the read data can be replaced or overwrittenwith the write data and then written into the cell. Thousands or evenmillions of these memory cells can be used to form a practical dynamicmemory device.

Following is a description regarding an exemplary method for sensing adatum “0” stored within a memory cell. FIG. 2 is a flowchartillustrating an exemplary method for accessing a datum represented by acharge stored in at least one memory cell of a memory circuit. FIG. 3 isa schematic drawing illustrating waveforms for accessing a memory cellstoring a datum “0”. Referring to FIGS. 1-3, a method 200 can access adatum represented by a charge stored in the memory cell 101 a of thememory circuit 100. In step 210, the bit line BL coupled with the memorycell 101 a can be precharged to the voltage that is substantially equalto or higher than the threshold voltage V_(t) of the transistor 111 ofthe sense amplifier 110.

In some embodiments, during the precharging period a voltage, e.g., VBB,(shown in FIG. 3) can be applied to the word line WL, turning off thememory transistor T_(c). A voltage, e.g., VBL, can be applied to globalbit line GBL and the signal line SL1. The voltage VBL can be, forexample, about 0.6 VDD, VDD/2, or other desired value. A voltage, e.g.,VPP, can be applied to the signal line SL2, turning on the transistor113. The turned-on transistor 113 can couple the bit line BL with theglobal bit line GBL. Since the global bit line GBL has been charged tothe voltage VBL, the voltage of the bit line BL can be pulled up towardthe voltage VBL. Since the capacitor C_(c) is free from including asubstantial charge for representing a datum “0”, the voltage of a nodebetween the capacitor C_(c) and the memory transistor T_(c) can besubstantially equal to 0, ground, or VSS.

After a desired time interval, the global bit line GBL can be floatingand the voltage of the signal line SL1 can be pulled down to a voltage,e.g., VSS. In some embodiments, the voltage of the bit line BL can bepulled up and higher than the threshold voltage V_(t) of the transistor111. In other embodiments, the voltage of the bit line BL can be pulledup to around VDD/2 (shown in FIG. 7). In still other embodiments, thevoltage of the bit line BL can be pulled up to a voltage between thethreshold voltage V_(t) of the transistor 111 and VDD/2. The pulled-upvoltage of the bit line BL can turn on the transistor 111. The turned-ontransistor 111 can couple the signal line SL1 with the global bit lineGBL. Since the voltage of the signal line SL1 is pulled down to thevoltage VSS, the voltage of the global bit line GBL can be pulled down.

Regarding the bit line BL, the turned-transistors 111 and 113 can couplethe bit line BL with the signal line SL1. Since the voltage of thesignal line SL1 is pulled down to the voltage VSS, the voltage of thebit line BL can be pulled down. As noted, the transistor 113 can havethe threshold voltage that is higher than that of the transistor 111 andthe bit line BL is coupled with the signal line SL1 through thetransistors 111 and 113. The voltage of the bit line BL can be pulleddown slightly. In some embodiments, the voltage of the bit line BL canbe pulled down slower than that of the global bit line GBL. The bit lineBL can be precharged to the voltage that is substantially equal to orhigher than the threshold voltage V_(t) of the transistor 111.

As noted, the bit line BL is precharged to the voltage that issubstantially equal to or higher than the threshold voltage V_(t) of thetransistor 111. The voltage of the signal line SL2 can be pulled down toa voltage, e.g., VSS, turning off the transistor 113. The turned-offtransistor 113 can desirably isolate the bit line BL from the global bitline GBL and the signal line SL1. The voltage of the bit line BL can bekept substantially equal to or higher than the threshold voltage V_(t)of the transistor 111. Since the voltage of the bit line BL can stillturn on the transistor 111, the voltage of the global bit line GBL canbe further pulled down to the voltage VSS.

Referring to FIGS. 1-3, in step 220 the bit line BL can be charge sharedwith the capacitor memory C_(c) of the cell 101 a. For charge sharing,the word line WL can be pulled up to a voltage, e.g., VPP, turning onthe memory transistor T_(c). The turned-on memory transistor T_(c) cancouple the capacitor C_(c) and the bit line BL. The charge of thecapacitor C_(c) and the charge on the bit line BL can be shared. Asnoted, the voltage of the node between the capacitor C_(c) and thememory transistor T_(c) is substantially equal to 0, the voltage of thenode can be pulled up. In contrary, the voltage of the charge-shared bitline BL is pulled down to a voltage that is smaller than the thresholdvoltage V_(t) of the transistor 111. The pulled-down voltage of thecharge-shared bit line BL can turn off the transistor 111.

Referring again to FIGS. 1-3, step 230 can sense the voltage of thecharge-shared bit line BL. In some embodiments sensing the voltage ofthe bit line BL, if the voltage of the charge-shared bit line is smallerthan the threshold voltage V_(t) of the transistor 111 of the senseamplifier 110, the datum stored within the memory cell 101 a canrepresent “0”.

For example, the voltage of the signal line SL1 can be pulled up to avoltage, e.g., VDD. As noted, the pulled-down voltage of thecharge-shared bit line BL turns off the transistor 111. The turned-offtransistor 111 can isolate the global bit line GBL from the signal lineSL1. The voltage of the global bit line GBL can be substantially freefrom being pulled up. A global sense amplifier GSA (not shown) can besubstantially free from sensing the voltage of the global bit line GBL.A datum “0” of the memory cell 101 a can be output. In some embodiments,the voltage of the global bit line GBL can be pulled up slightly due toleakages of the transistors 111 and/or 113. Since the pulled-up voltageof the global bit line GBL is substantially lower than a predeterminedvoltage level, the global sense amplifier GSA can be substantially freefrom sensing a voltage of the global bit line GBL. A datum “0” of thememory cell 101 a can still be output. In some embodiments, thepredetermined voltage level can be about 160 mV. In other embodiments,the predetermined voltage level can be about 100 mV. The values of thepredetermined voltage level are merely exemplary and the scope of theinvention is not limited thereto.

Following are descriptions regarding an exemplary method for sensing adatum “1” stored within a memory cell. FIG. 4 is a schematic drawingillustrating waveforms for accessing a memory cell storing a datum “1”.In some embodiments, the method 200 for accessing the memory cellstoring a datum “1” can precharge the bit line BL in the way similar tothat for accessing the memory cell storing a datum “0” described abovein conjunction with FIGS. 1-3. Since the capacitor C_(c) includes asubstantial charge for representing a datum “1”, the voltage of the nodebetween memory transistor T_(c) and the capacitor C_(c) can be high,e.g., about 0.9 V.

Referring to FIGS. 1-2 and 4, in step 220 the bit line BL can be chargeshared with the capacitor C_(c) of the memory cell 101 a. For chargesharing, the word line WL can be pulled up to a voltage, e.g., VPP,turning on the memory transistor T_(c). The turned-on memory transistorT_(c) can couple the capacitor C_(c) and the bit line BL. The charge ofthe capacitor C_(c) and the charge on the bit line BL can be shared. Asnoted, the voltage of the node between the capacitor C_(c) and thememory transistor T_(c) is high. The node can be pulled down. Incontrary, the voltage of the charge-shared bit line BL can be pulled upto a voltage that is higher than the threshold voltage V_(t) of thetransistor 111. The pulled-up voltage of the charge-shared bit line BLcan turn on the transistor 111.

Referring again to FIGS. 1-2 and 4, step 230 can sense the voltage ofbit line BL. In some embodiments sensing the voltage of the bit line BL,if the voltage of the charge-shared bit line is not smaller than thethreshold voltage V_(t) of the transistor 111 of the sense amplifier110, the datum stored within the memory cell 101 a can represent “1”.

For example, the voltage of the signal line SL1 can be pulled up to avoltage, e.g., VDD. As noted, the pulled-up voltage of the charge-sharedbit line BL turns on the transistor 111. The turned-on transistor 111can couple the global bit line GBL with the signal line SL1. The voltageof the global bit line GBL can be desirably pulled up. A global senseamplifier GSA (not shown) can substantially sense the pulled-up voltageof the global bit line GBL. A datum “1” of the memory cell 101 a can beoutput.

It is noted that the voltage levels, VBB, VSS, VDD, VPP, and/or VBLdescribed above in conjunction with FIGS. 3 and 4 are merely exemplary.The pull-up and/or pull-down of the voltage levels are also merelyexemplary. One of skill in the art can modify the waveforms andoperating sequences responding thereto to achieve a desired operationfor accessing data stored within the memory cell. It is also noted thatthe data “0” and “1” representing the memory cell with and withoutcharge, respectively, are merely exemplary. In some embodiments, aninverter can be added to the output of the global sense amplifier suchthat opposite data can be outputted.

As noted, the conventional 3-transistor single ended sense amplifierprecharges the bit line BL to the voltage VSS. The conventional3-transistor single ended sense amplifier has the issue of the thresholdvoltage variation of the NMOS sensing device. The routing of the readbit line RBL and the write bit line WBL of the conventional 3-transistorsingle ended sense amplifier is too complicated. The conventional3-transistor single ended sense amplifier has a large space between theNMOS transistors to accommodate the PMOS.

In contrary to the conventional 3-transistor single ended senseamplifier, the sense amplifier 110 can precharge the bit line BL to thevoltage that is substantially equal to or higher than the thresholdvoltage of the transistor 111 of the amplifier 110. The prechargedvoltage of the bit line BL can vary in responding to the change of thethreshold voltage of the transistor 111. If the threshold voltage of thetransistor 111 may be changed due to, for example, the variation of thesemiconductor manufacturing process, the precharged voltage of the bitline BL can change accordingly. The sense amplifier 110 can desirablyaccess data stored within memory cells of the memory circuit.

It is found that the sense amplifier 110 is free from including therouting of the read bit line RBL and the write bit line WBL of theconventional 3-transistor single ended sense amplifier. The routing ofthe bit line portion of the sense amplifier 110 can be desired. It isalso found that the sense amplifier 110 can be free from including thePMOS transistor of the conventional 3-transistor single ended senseamplifier. The area of the sense amplifier 110 can be desirably reduced.

FIG. 5 is a schematic drawing illustrating another exemplary memorycircuit including a precharge transistor. Items of FIG. 5 that are thesame items in FIG. 1 are indicated by the same reference numerals,increased by 400. In FIG. 5, a memory circuit 500 can include aprecharge transistor 520 coupled with the bit line BL. A gate of theprecharge transistor 520 can be coupled with a signal line SL3. A S/D520 a of the precharge transistor 520 can be coupled with the bit line.Another S/D 520 of the precharge transistor 520 can be coupled with aground or VSS.

In some embodiments, before step 210 (shown in FIG. 2) a voltage of thesignal line SL3 can be pulled up to a voltage, e.g., VDD, turning on theprecharge transistor 520. The turned-on precharge transistor 520 cancouple the bit line BL with ground or VSS for discharging a charge ofthe bit line BL. The charge may be resulted from, e.g., leakages of thetransistors 511, 513, and/or the memory transistor T_(c).

FIG. 6 is a schematic drawing showing a system including an exemplarymemory circuit. In FIG. 6, a system 600 can include a processor 610coupled with the memory circuit 601. The memory circuit 601 can besimilar to the memory circuit 100 or 500 described above in conjunctionwith FIGS. 1 and 5. The processor 610 is capable of accessing the datumstored in the memory cell of the memory circuit 601. In someembodiments, the processor 610 can be a processing unit, centralprocessing unit, digital signal processor, or other processor that issuitable for accessing data of memory circuit.

In some embodiments, the processor 610 and the memory circuit 601 can beformed within a system that can be physically and electrically coupledwith a printed wiring board or printed circuit board (PCB) to form anelectronic assembly. The electronic assembly can be part of anelectronic system such as computers, wireless communication devices,computer-related peripherals, entertainment devices, or the like.

In some embodiments, the system 600 including the memory circuit 100 canprovide an entire system in one IC, so-called system on a chip (SOC) orsystem on integrated circuit (SOIC) devices. These SOC devices mayprovide, for example, all of the circuitry needed to implement a cellphone, personal data assistant (PDA), digital VCR, digital camcorder,digital camera, MP3 player, or the like in a single integrated circuit.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A memory circuit comprising: at least one memorycell for storing a charge representative of a datum, the memory cellbeing coupled with a word line and a bit line; and a sense amplifiercoupled with the bit line, the sense amplifier being capable ofprecharging the bit line to a first voltage that is substantially equalto or higher than a threshold voltage (V_(t)) of a first transistor ofthe sense amplifier, wherein a gate of the first transistor is coupledwith the bit line, and a first source/drain of the first transistor iselectrically coupled with a global bit line.
 2. The memory circuit ofclaim 1, wherein the first voltage is between about the thresholdvoltage (V_(t)) of the first transistor and half of an internal powervoltage (VDD).
 3. The memory circuit of claim 2, wherein the senseamplifier is capable of precharging the bit line to a second voltagethat is substantially equal to half of the internal power voltage VDDbefore precharging the bit line to the first voltage that issubstantially equal to or higher than the threshold voltage (V_(t)) ofthe first transistor of the sense amplifier.
 4. The memory circuit ofclaim 1, wherein a second source/drain of the first transistor iscoupled with a first signal line.
 5. The memory circuit of claim 4,wherein the sense amplifier further comprises: a second transistor, thesecond transistor having a first source/drain coupled with the globalbit line, a second source/drain coupled with the bit line, and a gatecoupled with a second signal line.
 6. The memory circuit of claim 5,wherein a threshold voltage of the second transistor is higher than thethreshold voltage (V_(t)) of the first transistor.
 7. The memory circuitof claim 1 further comprising a third transistor coupled with the bitline, wherein the third transistor is capable of discharging a charge ofthe bit line BL before the sense amplifier precharging the bit line tothe first voltage.
 8. A system comprising: a memory circuit comprising:at least one memory cell for storing a charge representative of a datum,the memory cell being coupled with a word line and a bit line; and asense amplifier coupled with the bit line, the sense amplifier beingcapable of precharging the bit line to a first voltage that issubstantially equal to or higher than a threshold voltage (V_(t)) of afirst transistor of the sense amplifier, a gate of the first transistoris coupled with the bit line, and a first source/drain of the firsttransistor is electrically coupled with a global bit line; and aprocessor coupled with the memory circuit for accessing the datum storedin the at least one memory cell.
 9. The system of claim 8, wherein thefirst voltage is between about the threshold voltage V_(t) of the firsttransistor and half of an internal power voltage (VDD).
 10. The systemof claim 9, wherein the sense amplifier is capable of precharging thebit line to a second voltage that is substantially equal to half of theinternal power voltage VDD before precharging the bit line to the firstvoltage that is substantially equal to or higher than the thresholdvoltage (V_(t)) of the first transistor of the sense amplifier.
 11. Thesystem of claim 8, wherein a second source/drain of the first transistoris coupled with a first signal line.
 12. The system of claim 11, whereinthe sense amplifier further comprises: a second transistor, the secondtransistor having a first source/drain coupled with the global bit line,a second source/drain coupled with the bit line, and a gate coupled witha second signal line.
 13. The system of claim 12, wherein a thresholdvoltage of the second transistor is higher than the threshold voltage(V_(t)) of the first transistor.
 14. The system of claim 8 furthercomprising a third transistor coupled with the bit line, wherein thethird transistor is capable of removing a charge of the bit line BLbefore the sense amplifier precharging the bit line to the firstvoltage.
 15. A method for accessing a datum represented by a chargestored in at least one memory cell of a memory circuit, the methodcomprising: precharging a bit line coupled with the at least one memorycell to a first voltage that is substantially equal to or higher than athreshold voltage (V_(t)) of a sensing device of a sense amplifier,wherein precharging the bit line comprises selective coupling anddecoupling a global bit line and a signal line by controlling atransistor using the bit line, a gate of the transistor connected to thebit line, a first source/drain of the transistor electrically connectedto the global bit line.
 16. The method of claim 15, wherein the firstvoltage is between about the threshold voltage V_(t) of the sensingdevice and half of an internal power voltage (VDD).
 17. The method ofclaim 15 further comprising: charge sharing the bit line and the chargestored in the at least one memory cell; and sensing a voltage of thecharge-shared bit line, wherein the datum stored within the at least onememory cell represents “0”, if the voltage of the charge-shared bit lineis smaller than the threshold voltage (V_(t)) of the sensing device ofthe sense amplifier; and the datum stored within the at least one memorycell represents “1”, if the voltage of the charge-shared bit line is notsmaller than the threshold voltage (V_(t)) of the sensing device of thesense amplifier.
 18. The method of claim 15 further comprising:precharging the bit line to a second voltage that is substantially equalto half of an internal power voltage (VDD) before precharging the bitline to the first voltage that is substantially equal to or higher thanthe threshold voltage (V_(t)) of the sensing device of the senseamplifier.
 19. The method of claim 15 further comprising: discharging acharge of the bit line BL before precharging the bit line to the firstvoltage.
 20. The method of claim 15, wherein selectively coupling anddecoupling the global bit line and the signal line further comprises: asecond source/drain of the transistor is connected to the signal line.